paper 1: NASA ADS, astro-ph

paper 2: in prep

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Travel 2009-10:

June 19-30: Prato, Italy
Linfest

July 1-5: Tenerife, Spain
Talk at IAC

July 12-Aug 24: Princeton, NJ
PiTP 2009: Computational Astrophysics

July 30-Aug 8: La Serena, Chile
Observations at CTIO

Aug 10-15: Rio de Janeiro, Brazil
IAU General Assembly

Jan 02-09: Washington, DC
Talk at AAS Meeting
 Massive Black Hole Recoil in High Resolution Hosts

Javiera Guedes, Piero Madau, Michael Kuhlen, Jurg Diemand, Marcel Zemp, Lucio Mayer and Simone Callegari.

   Numerical relativistic codes are now able follow the orbits of black holes from inspiral to merger. Back in the 60’s, Peres suggested that asymmetries in the configuration black hole binaries (different masses or spins) would have the net effect of beaming gravitational wave radiation in some preferred direction, a problem theoretically analog to electromagnetic radiation recoil. In the gravitational case the recoil arises from the interference of the mass quadrupole and the mass octopole (or alternatively, the flow quadrupole radiation.) The magnitude of the kick velocity depends on: a) the mass ratio of the binary, b) the spin magnitudes and c) spin orientations. The Baker et al. 2008 numerical fit looks like this:

where mu = q/(q+1) and q =m1/m2 < 1, A,B,H,K, and Phi_i are constants. The maximum possible recoil of velocity V = 3,750 km/s can be achieved when the black holes in the binary have equal masses and their spin vectors are maximally-rotating and counter-aligned (Campanelli et al. 2007). Less rare recoil velocity distributions are given by Baker et al. 2008 Table 3 and in Figure 2 of Tanaka and Haiman 2009 (a very nice paper, sans possible typo in equation 12.) The above configuration can be represented schematically by the figure below.

There are several aspects of the recoil process that are still unclear, such as its effect on the cosmological build up of massive black holes from seeds expected to exist as early as z=20 to the SMBHs we see at the centers of galaxies today. Due to the recoil kick imparted to merging black holes by the gravitational-wave radiation, the remnant black holes are launched into orbits that depend on the details of the host potential:

a) In spherical bulges the black hole will oscillate right through the center, and return to the center after a few dynamical times, or deplete or "heat up" the stars in the nucleus, reducing the efficiency of dynamical and extending the return time.

b) If the black hole is able to leave the bulge and enters a triaxial dark matter halo, it may not return at all within a Hubble time (we recently published a paper that looks at this in detail.)

c) High resolution simulations of gas mergers (e.g. Mayer et al. 2007) show that up to 60% of the initial gas is funneled to the center of the remnant. In that particular simulation, the mass of the nuclear disk is Md = 3e9 Msun, and recoling black holes with velocities of ~500 km/s are not able to escape the central region (scale length L=75 pc).

A movie of a black hole recoiling with initial kick velocity V=1200 km/s in the direction perpendicular to the nuclear disk is shown below. Click for movie.

Because the majority of black holes merge at high redshifts, detection becomes difficult. The most commonly used technique to find off-set AGN / QSOs is to look for shifts between the broad-line region associated with the QSO and the narrow-line region associated with the starlight from the galaxy. Unfortunately no recoil candidate has been confirmed (one must be brave to report a recoiling SMBH these days, since their paper will be heavily cited by people suggesting alternative hypotheses.)